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United States Patent |
5,314,145
|
Rauckhorst, III
|
May 24, 1994
|
Compressible nose dynamic de-icer
Abstract
A de-icer comprises a compressible member immediately subjacent an outer
skin overlying an apex of a leading edge. The compressible member
facilitates deflection of the outer skin overlying the compressible member
toward the substructure when the skin deflection means deflects the outer
skin.
Inventors:
|
Rauckhorst, III; Richard L. (North Canton, OH)
|
Assignee:
|
The B.F. Goodrich Company (Akron, OH)
|
Appl. No.:
|
998283 |
Filed:
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December 30, 1992 |
Current U.S. Class: |
244/134A |
Intern'l Class: |
B64D 015/18 |
Field of Search: |
244/134 R,134 A
|
References Cited
U.S. Patent Documents
3604666 | Sep., 1971 | Achberger | 244/134.
|
4516745 | May., 1985 | Ely et al. | 244/134.
|
4595442 | Jun., 1986 | Trares et al. | 244/134.
|
4678144 | Jul., 1987 | Goehner et al.
| |
4706911 | Nov., 1987 | Briscoe et al.
| |
4875644 | Oct., 1989 | Adams et al.
| |
5098037 | Mar., 1992 | Leffel et al. | 244/134.
|
5129598 | Jul., 1992 | Adams et al. | 244/134.
|
5143325 | Sep., 1992 | Zieve et al.
| |
Other References
WO81/00993 Blaser et al, Apr. 1981.
|
Primary Examiner: Barefoot; Galen L.
Attorney, Agent or Firm: Leffel; Kevin L.
Claims
I claim:
1. A de-icer adapted for attachment to a substructure having an apex where
the radius of curvature of the substructure is smallest, the de-icer
having an outer surface subjected to an impinging airstream, comprising:
skin means for transferring tension from a first area of said skin means to
a second area of said skin means upon deflection of said first area away
from the substructure, said skin means overlying the substructure with
said first area spaced to one side of the apex and said second area at the
apex;
skin deflection means disposed beneath said skin means for deflecting said
skin means away from the substructure;
compressible means disposed beneath said second area for permitting
deflection of said second area toward the substructure by compressing in
response to tension transferred by said skin means from said first area to
said second area upon deflection of said first area away from the
substructure.
2. The de-icer of claim 1 wherein said compressible means divides said skin
deflection means, said compressible means being immediately subjacent said
skin means, and said skin deflection means abuts said compressible means.
3. The de-icer of claim 1 wherein said skin deflection means overlies said
compressible means, said skin deflection means being immediately subjacent
said skin means.
4. The de-icer of claims 1, 2 or 3 wherein said compressible means is
comprised of an elastomer.
5. The de-icer of claims 1, 2 or 3 wherein said compressible means is
comprised of butyl rubber.
6. The de-icer of claim 5 wherein said compressible means has a thickness
between about 0.05 and 0.1 inch.
7. The de-icer of claim 1, 2 or 3 wherein said skin means includes at least
one layer of fiber reinforced plastic that selectively stiffens said skin
means in a predetermined area.
8. The de-icer of claim 1, 2, or 3 wherein said skin means includes at
least one layer of fabric impregnated with nitrile phenolic matrix, the
fibers of said fabric layer being selected from a group consisting of
carbon fibers, glass fibers, nylon fibers, and aramid fibers.
9. The de-icer of claim 2 wherein the substructure has a chordwise
direction generally parallel to the direction of the impinging airstream
and a spanwise direction in which the substructure extends generally
perpendicular to the chordwise direction, and said skin deflection means
comprises at least two expandable tubes extending in the spanwise
direction, one each on either side of said compressible means, each said
tube abutting said compressible means.
10. The de-icer of claim 3 wherein the substructure has a chordwise
direction generally parallel to the direction of the impinging airstream
and a spanwise direction in which the substructure extends generally
perpendicular to the chordwise direction, and said skin defection means
comprises at least two expandable tubes extending in the spanwise
direction, said tubes abutting each other over said compressible means.
11. The de-icer of claim 3 wherein the substructure has a chordwise
direction generally parallel to the direction of the impinging airstream
and a spanwise direction in which the substructure extends generally
perpendicular to the chordwise direction, and said skin deflection means
comprises at least three expandable tubes extending in the chordwise
direction, one tube overlying said compressible means, the other two tubes
being disposed on either side of and abutting said tube overlying said
compressible means.
12. The de-icer of claim 9 wherein said skin deflection means further
comprises at least a third expandable tube extending in the spanwise
direction abutting one of said previous two tubes, said abutting tubes
partially overlapping in the chordwise direction.
13. The de-icer of claim 1 wherein said skin deflection means comprises
electromagnetic apparatus, said electromagnetic apparatus being of the
type that utilizes a high magnitude short duration current pulse to
develop opposing electromagnetic fields that cause said skin means to be
deflected from the substructure.
14. The de-icer of claim 13 wherein said electromagnetic apparatus includes
at least one coil, said high magnitude short duration current pulse being
applied to each coil, each coil including:
a first, sheet-like member defined by a first, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said first conductor defining an electrical input and said
second end of said first conductor defining an electrical output;
a second, sheet-like member defined by a second, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said second conductor defining an electrical input, and said
second end of said second conductor defining an electrical output;
an electrical connection between said second end of said first conductor
and said first end of said second conductor; and
said first and second sheet-like members being disposed parallel to each
other with selected turns of said first electrical conductor being
positioned adjacent to selected turns of said second electrical conductor
such that said direction of current flow through the turns of said first
conductor is in the same direction as the current flow through the turns
of said second conductor.
15. The de-icer of claim 14 wherein said electromagnetic apparatus
comprises at least two coils, one each on either side of said compressible
means, each coil abutting said compressible means.
16. The de-icer of claim 15 wherein at least one coil is formed as an
integral part of said skin means.
17. The de-icer of claim 13 wherein said skin means includes at least one
layer of fabric impregnated with nitrile phenolic matrix, the fibers of
said fabric layer being selected from a group consisting of carbon fibers,
glass fibers, nylon fibers, and aramid fibers.
18. The de-icer of claim 14 wherein said thin compressible means is
comprised of butyl rubber.
19. The de-icer of claim 18 wherein said thin compressible means has a
thickness of between about 0.05 and 0.1 inch.
20. The de-icer of claim 14 further comprising a target adjacent each coil,
said target being superposed over said coil, said coil being separable
from said target, one of the opposing electromagnetic fields being
developed by said coil upon application of said high magnitude short
duration current pulse and the other opposing electromagnetic field being
developed in said target by eddy currents induced by said coil
electromagnetic field.
21. The de-icer of claim 14 further comprising at least two coils, said
coils being adjacent each other with one coil superposed over said other
coil, said coils being separable from each other, one of the opposing
electromagnetic fields being developed upon application of said high
magnitude short duration current pulse to one coil and the other opposing
electromagnetic field being developed upon application of said high
magnitude short duration current pulse to said other coil, said coils
being electrically interconnected such that current direction in said
selected turns of said conductor of one coil is opposite to said current
direction in said selected turns of said conductor of said other coil.
22. The de-icer of claim 3 wherein said skin deflection means includes
electromagnetic apparatus, said electromagnetic apparatus being of the
type that utilizes a high magnitude short duration current pulse to
develop opposing electromagnetic fields that cause said skin to be
deflected from the substructure, the electromagnetic apparatus comprising
at least two coils abutting each other along an edge overlying the apex,
said high magnitude short duration current pulse being applied to each
coil, each coil including:
a first, sheet-like member defined by a first, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said first conductor defining an electrical input and said
second end of said first conductor defining an electrical output;
a second, sheet-like member defined by a second, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said second conductor defining an electrical input, and said
second end of said second conductor defining an electrical output;
an electrical connection between said second end of said first conductor
and said first end of said second conductor; and
said first and second sheet-like members being disposed parallel to each
other with selected turns of said first electrical conductor being
positioned adjacent to selected turns of said second electrical conductor
such that the direction of current flow through the turns of the first
conductor is in the same direction as the current flow through the turns
of the second conductor.
23. The de-icer of claim 3 wherein said skin deflection means includes
electromagnetic apparatus, said electromagnetic apparatus being of the
type that utilizes a high magnitude short duration current pulse to
develop opposing electromagnetic fields that cause said skin to be
deflected from the substructure, said electromagnetic apparatus comprising
at least three coils, one coil overlying said compressible means in
between and abutting said other two coils, said high magnitude short
duration current pulse being applied to each coil, each coil including:
a first, sheet-like member defined by a first, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said first conductor defining an electrical input and said
second end of said first conductor defining an electrical output;
a second, sheet-like member defined by a second, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said second conductor defining an electrical input, and said
second end of said second conductor defining an electrical output;
an electrical connection between said second end of said first conductor
and said first end of said second conductor; and
said first and second sheet-like members being disposed parallel to each
other with selected turns of said first electrical conductor being
positioned adjacent to selected turns of said second electrical conductor
such that the direction of current flow through the turns of said first
conductor is in the same direction as the current flow through the turns
of said second conductor.
24. The de-icer of claim 1 wherein said skin deflection means is further
for deflecting said skin means away from the substructure with a peak
acceleration of at least about 3000 g's.
25. The de-icer of claim 1 wherein said skin deflection means is further
for deflecting said skin means away from the substructure at a rate of at
least about 2000 Hz.
26. The de-icer of claim 1 wherein said skin deflection means is further
for deflecting said skin means away from the substructure between about
0.02 inch and 0.06 inch.
27. The de-icer of claim 1 wherein said skin means has a modulus of
elasticity of at least 40,000 kPa.
28. The de-icer of claim 1 wherein said compressible means has a durometer
of less than about a Shore A 90.
29. The de-icer of claim 1 wherein said compressible means has a durometer
between about a Shore A55 and a Shore A 65.
30. The de-icer of claim 1 wherein said skin means comprises a fabric
layer.
31. The de-icer of claim 30 wherein said fabric layer transfers tension
from said first area to said second area upon deflection of said first
area away from the substructure.
32. A method of deicing a substructure having an apex where the radius of
curvature of the substructure is smallest, the method comprising the steps
of:
a) providing a deflectable skin over the substructure;
b) providing a compressible member at the apex beneath said deflectable
skin;
c) deflecting said deflectable skin away from the substructure with an
attendant deflection of said deflectable skin over the apex toward the
substructure resisted by compression of said compressible member.
33. The method of claim 32 wherein the step of deflecting said deflectable
skin away from the substructure occurs with a peak acceleration of at
least about 3000 g's.
34. The method of claim 32 wherein the step of deflecting said deflectable
skin away from the substructure occurs at a rate of at least about 2000
Hz.
35. The method of claim 32 wherein the step of deflecting said deflectable
skin away from the substructure occurs with a deflection between about
0.02 inch and 0.06 inch.
36. A method of de-icing a substructure having an apex where the radius of
curvature of the substructure is smallest, the method comprising the steps
of:
a) providing a deflectable skin over the substructure;
b) providing a compressible member at the apex beneath said deflectable
skin;
b) developing tension in said deflectable skin by deflecting said
deflectable skin away from the substructure over an area spaced to one
side of the apex;
c) transferring said tension to the apex from said area spaced to one side
of the apex;
d) deflecting said skin overlying the apex toward the substructure resisted
by compression of said compressible member in response to said tension
transferred to the apex.
37. The method of claim 36 wherein the step of deflecting said deflectable
skin away from the substructure over an area spaced to one side of the
apex occurs with a peak acceleration of at least about 3000 g's.
38. The method of claim 36 wherein the step of deflecting said deflectable
skin away from the substructure over an area spaced to one side of the
apex occurs at a rate of at least about 2000 Hz.
39. The method of claim 36 wherein the step of deflecting said deflectable
skin away from the substructure over an area spaced to one side of the
apex occurs with a deflection between about 0.02 inch and 0.06 inch.
40. A method of de-icing a substructure having an apex where the radius of
curvature of the substructure is smallest, the method comprising the steps
of:
a) providing a deflectable skin over the substructure;
b) providing a compressible member at the apex beneath said deflectable
skin; and
b) deflecting said deflectable skin away from the substructure over an area
spaced to one side of the apex by stretching said deflectable skin and by
compressing said compressible member.
41. The method of claim 40 wherein the step of deflecting said deflectable
skin away from the substructure over an area spaced to one side of the
apex occurs with a peak acceleration of at least about 3000 g's.
42. The method of claim 40 wherein the step of deflecting said deflectable
skin away from the substructure over an area spaced to one side of the
apex occurs at a rate of at least about 2000 Hz.
43. The method of claim 40 wherein the step of deflecting said deflectable
skin away from the substructure over an area spaced to one side of the
apex occurs with a deflection between about 0.02 inch and 0.06 inch.
Description
FIELD OF THE INVENTION
This invention relates to a class of de-icers that utilize dynamic motion
to expel ice accumulated on various aircraft surfaces during flight in
atmospheric icing conditions. Particularly, this invention relates to a
mechanical de-icer of the type that utilize skin deflection means to
dynamically activate a thin deflectable outer skin upon which ice
accumulates. The invention comprises a compressible member immediately
subjacent the skin overlying an area having the smallest radius of
curvature on a leading edge.
BACKGROUND OF THE INVENTION
In recent years, many aircraft manufacturers have sought improved ice
protection systems to enable aircraft to safely fly in atmospheric icing
conditions. Ice accumulations on the leading edge surfaces of various
aircraft structures can seriously effect the aerodynamic characteristics
of an aircraft. Examples of such aircraft structures include wings, engine
inlets, and horizontal and vertical stabilizers. A leading edge is that
portion of a surface of a structure that functions to meet and break an
airstream impinging upon the surface of an aircraft structure. The
impinging airstream is induced during flight. Conventional pneumatic
de-icers, electrothermal de-icers and bleed air anti-icers have been used
for many years to protect the leading edges of general aviation or
commercial aircraft. These ice protection techniques are described in
detail by Technical Report ADS-4, Engineering Summary of Airframe Icing
Technical Data published by the Federal Aviation Agency, December 1963. In
spite of these proven techniques, many aircraft manufacturers and
operators have expressed a desire for new systems having better ice
removal performance, longer life and decreased weight and energy
requirements.
In response to this need, a class of systems has been developed that
utilize skin deflection means to dynamically activate a thin deflectable
outer skin upon which ice accumulates. The dynamic activation induces
rapid motion in the thin deflectable skin sufficient to dynamically
debond, shatter and expel an accumulated ice cap into surrounding airflow.
As will be discussed more fully, the skin deflection means can take a
variety of forms.
In some devices, the skin deflection means are combined with the thin
deflectable outer skin to form a unitary de-icer. The unitary de-icer is
generally formed in a thin sheet that can be subsequently bonded to the
leading edge surface of an existing aircraft structure. The de-icer is
usually designed to be removed from the aircraft structure and replaced in
the field requiring the use of a replaceable adhesive such as 3M 1300L
rubber cement. Examples are presented in U.S. Pat. No. 4,706,911 METHOD
AND APPARATUS FOR DEICING A LEADING EDGE, Briscoe et. al. (hereinafter
referred to as the Pneumatic Impulse Patent), U.S. Pat. No. 4,875,644
ELECTRO-REPULSIVE SEPARATION SYSTEM FOR DEICING, Adams et al. (hereinafter
referred to as the Electro-Repulsive Patent), and U.S. Pat. No. 5,129,598
ATTACHABLE ELECTRO-IMPULSE DE-ICER, Adams et al. (hereinafter referred to
as the Electro-Impulse Patent). In other devices, the skin deflection
means are combined with the thin deflectable outer skin and a reinforcing
structure thereby forming a unitary leading edge structure with integral
de-icing capability. The de-icer is permanently bonded to the reinforcing
structure necessitating replacement of the entire assembly upon failure of
the de-icer. An example of this type of device is presented in U.S. Pat.
No. 5,098,037 STRUCTURAL AIRFOIL HAVING INTEGRAL EXPULSIVE SYSTEM, Leffel
et al. (hereinafter referred to as the Integral Expulsive System Patent).
For the purposes of this application, the structure to which the de-icer
is attached will be referred to as the "substructure." Examples of
substructures include an existing aircraft structure having a leading edge
surface and a reinforcing structure as discussed above.
As mentioned previously, the skin deflection means can take a variety of
forms. In the Electro-Repulsive Patent, the skin deflection means
comprises an upper array of conductors and a lower array of conductors.
The upper conductors are substantially parallel to each other and to
adjacent conductors in the lower layer. The upper conductors are connected
in series with the lower conductors so that a single continuous conductor
is formed that passes from the upper layer, around the lower layer, back
around the upper layer, and so on. Upon application of an electrical
potential to the input leads, current is developed in the upper conductors
that is in the same direction in all upper conductors. Likewise, current
is developed in the lower conductors that is in the same direction in all
lower conductors, but opposite to the direction of the current in the
upper conductors. As explained in the Electro-Repulsive Patent,
maintaining a constant current direction in all the conductors of a layer
greatly increases the separation force between the two layers.
After installation of the de-icer on a substructure, the upper and lower
conductors are sandwiched between the structural member and a surface ply
(the surface ply is analogous to a thin deflectable skin). Upon
application of a high magnitude short duration current pulse, opposing
electromagnetic fields in the upper and lower layers forcefully repel each
other. This motion induces a dynamic motion into the surface ply which
dynamically removes accumulated ice. As described in the Electro-Repulsive
Patent, a current pulse that rises to between 2300 and 3100 amperes within
100 microseconds generates effective ice removal. A circuit for generating
such a pulse is described in the Electro-Repulsive Patent. The circuit
includes a pulse forming network, but this is not absolutely necessary.
Another form for the skin deflection means utilizing electromagnetic
apparatus is illustrated by the Electro-Impulse Patent. A planar coil
comprising at least one coiled conductor is sandwiched between a surface
ply and a conductive substructure (such as the leading edge of an aluminum
aircraft structure). Planar coils are described in great detail in U.S.
Pat. No. 5,152,480 PLANAR COIL CONSTRUCTION, Adams et al. (hereinafter
referred to as the Planar Coil Patent). As described in the
Electro-Impulse Patent, a high magnitude short duration current pulse is
applied to the coil. The current in the coil induces a strong rapidly
changing electromagnetic field. The electromagnetic field generates eddy
currents in the conductive substructure which, in turn, generates an
opposing electromagnetic field. The two electromagnetic fields repel each
other causing a repelling force between the coil and the substructure. The
coil induces dynamic motion into the surface ply thereby dynamically
removing accumulated ice. Effective ice removal is generated by a peak
current of about 3000 amperes rising in a period of 100 microseconds. An
electrical circuit for generating such a pulse is disclosed. The circuit
is very similar to the circuit disclosed in the Electro-Repulsive Patent.
In the previous example, the skin deflection means is composed of a single
unitary planar coil. A target may also be required if the substructure
does not have sufficient electrical conductivity to effectively develop
eddy currents. A target would be required with a fiber reinforced plastic
substructure, or a conductive substructure that is too thin to effectively
develop eddy currents. The target is a sheet of conductive material such
as copper or aluminum that is located adjacent one surface of the coil.
The coil and target are forcefully repelled from each other upon
application of a high magnitude short duration current pulse to the coil
due to opposing magnetic fields generated by current in the coil and by
eddy currents in the target. This motion induces dynamic motion into the
surface ply which dynamically removes accumulated ice. The target can be
formed as a part of the substructure or can be formed as a part of the
thin force and displacement generation means. Also, as described in the
Electro-Impulse Patent, either the target or the coil can be located
immediately subjacent the outer skin. The target applies the motive force
to the skin if it is located subjacent the skin. Conversely, the coil
applies the motive force to the skin if it is located subjacent the skin.
The Planar Coil Patent also teaches an electro-repulsive variation similar
to the Electro-Repulsive Patent. Two mirror image unitary planar coils are
superposed relative to each other and electrically connected so that upon
application of a high magnitude short duration current pulse to each coil,
current direction is opposite in each coil. Opposing electromagnetic
fields are generated in the coils which causes each coil to forcefully
repel the other. This motion induces a mechanical impulse into the surface
ply which removes accumulated ice. This approach differs from the
Electro-Repulsive Patent which utilizes a single conductor to form the
upper and lower conductors.
A type of skin deflection means that utilizes pressurized gas is described
in the Pneumatic Impulse Patent and the Integral Expulsive System Patent.
A plurality of pneumatic impulse tubes extend in a spanwise direction
subjacent a thin deflectable outer skin. The tubes and skin are supported
by a fiber reinforced plastic substructure which together form a leading
edge structure with integral de-icing capability. Special fittings are
integrated into the tubes at various locations spaced along the span of
each tube. A pneumatic impulse valve is attached to each fitting. A
suitable valve is described in U.S. Pat. No. 4,878,647 PNEUMATIC IMPULSE
VALVE AND SEPARATION SYSTEM, Putt et al. The valve contains a small volume
(about 1 cubic inch) of high pressure air (500 to 5,000 psig). Upon
activation by a solenoid, the valve quickly releases the pressurized air
into each tube via the fitting. The expanding air pulse causes the tube to
expand and induce mechanical motion into the skin thereby dynamically
expelling accumulated ice. The expanding air pulse most preferably
inflates the tube in less than 500 microseconds.
As evidenced by these patents, many variations of skin deflection means
have been developed. The Electro-Repulsive Patent, Electro-Impulse Patent,
Planar Coil Patent, Pneumatic Impulse Patent, and Integrated Pneumatic
Impulse Patent provide examples of the types of structure that can serve
as skin deflection means. In each example, the skin deflection means
generates a force that causes the skin to be deflected away from the
substructure. These patents are intended to be merely representative, and
the types of structures that can serve as skin deflection means is not
limited to the specific teachings of these patents.
Certain devices in the art are presented in FIGS. 1 and 2. The de-icers of
FIGS. 1 and 2 have skin deflection means of the type that utilize
compressed air as described by the Pneumatic Impulse Patent and Integral
Expulsive System Patent. Unless noted otherwise, the following discussion
applies equally as well to skin deflection means that utilize
electromagnetic apparatus similar to those presented in the
Electro-Repulsive Patent, Electro-Impulse Patent, and Planar Coil Patent.
Referring to FIG. 1, a de-icer 100 is shown attached to a substructure 102
which serves to support the de-icer 100. An outer surface 122 meets and
breaks an impinging airstream 119. Ice cap 115 is deposited by the
airstream 119 during flight in atmospheric icing conditions. The section
shown in FIG. 1 is a chordwise cross-section. The chordwise direction is
defined as being approximately parallel to the direction of the impinging
airstream 119 as it passes around the de-icer 100 and substructure 102.
The de-icer 100 and substructure 102 also extend in a spanwise direction
which is generally perpendicular to the chordwise direction. The de-icer
and substructure can either be straight or have curvature in the spanwise
direction. If de-icer 100 is applied to an engine inlet, the spanwise
direction corresponds to the circumference of the inlet. In practicing the
invention, the spanwise curvature can generally be ignored. Therefore, for
the purposes of this application, the term "curvature" refers only to
curvature measured in the plane of the chordwise section.
The outer surface 122 has a radius of curvature R that changes depending on
the chordwise position along the outer surface 122. The radius of
curvature R is measured perpendicular to the outer surface 122 in a
chordwise plane. De-icer 100 and substructure 102 have an apex 120. The
term "apex" is intended to refer to the portion of a de-icer and
substructure underlying the area of the outer surface where the radius of
curvature is smallest. The outer surface 122 defines a typical curvature
wherein the smallest radius of curvature R is over the apex 120 and the
radius of curvature R increases with distance from the apex 120.
De-icer 100 is comprised of a skin 104 and skin deflection means 103.
Substructure 102 can be formed from metal, such as aluminum, or from fiber
reinforced plastic, such as a plurality of reinforcing plies impregnated
with plastic matrix (for example, plies of fabric formed from carbon,
glass, or Kevlar.RTM. fibers impregnated with epoxy resin). The outer
surface of the de-icer forms the outer surface 122.
The thin deflectable skin 104 is composed of an erosion resistant layer 105
and a backing layer 106. The erosion resistant layer can be formed from
nearly any film having good erosion resistant properties. Titanium 15-3
alloy 0.005 inch thick and polyether-ether-ketone (PEEK) ranging from
0.007 to 0.016 inch thick have been used for erosion layer 105. The
backing layer 106 can either support and reinforce the erosion layer, or
it can serve to bond the erosion layer to the skin deflection means 103.
Epoxy and nitrile phenolic film adhesives have been used for the backing
layer 106.
The skin deflection means 103 has five expandable tubes 107.varies.111 that
abut each other along an edge of each tube. Tubes 107-111 can be formed
from plastic coated fabric, such as nitrile phenolic impregnated nylon
fabric, or from rubber coated fabric such as neoprene coated nylon fabric.
The tubes 107-111 are described in greater detail in the Pneumatic Impulse
Patent and Integral Expulsive System Patent. One tube 109 overlies the
apex 120. Tube 110 is shown inflated. Deflections of skin 104 over tubes
108 and 109 are shown by phantom lines 112 and 113 respectively. Tubes
107-111 are sequentially inflated by pulses of compressed air as described
in the Pneumatic Impulse Patent or Integral Expulsive System Patent.
Inflation of the tubes 107-111 induces dynamic motion in the skin 104 and
ice cap 115 is debonded and shattered into side ice-pieces 116 and 118,
and nose ice-piece 117, which are ejected into impinging airstream 119.
Centerline 121 bisects the de-icer 100 and substructure 102. Depending on
the angle of the incoming airflow in relation to the centerline 121, ice
accumulation 115 could shift to predominantly one surface or the other.
For example, if the incoming airflow rotates to below the centerline 121,
the ice cap would shift back over tube 107 and forward over only part of
tube 110. The amount of shift depends on the magnitude of the angle
between the incoming airflow 119 and the centerline 121 which is a
function of aircraft flight and airflow characteristics. Tubes 107 and 111
are provided to protect against shifts in the ice cap 115. They are
normally activated sequentially with tubes 108-110 as part of a single
activation cycle.
Referring now to FIG. 2, de-icer 200 represents another arrangement for the
skin deflection means. De-icer 200 is shown attached to substructure 202
that has an apex 220. De-icer 200 comprises skin 204 and skin deflection
means 203. The de-icer 200 and substructure 202 are bisected by a
centerline 221, and de-icer 200 has an outer surface 222. The outer
surface 222 has a radius of curvature R that changes with distance from
the apex 220. Here, the skin deflection means 203 has only four tubes 207,
208, 210 and 211 arranged such that the edges of tubes 208 and 210 abut
directly over the apex 220. Skin 204 includes a backing layer 206 and an
erosion resistant layer 205. The substructure 202, skin deflection means
203 and skin 204 can be constructed from the same materials as the
substructure 102, skin deflection means 103 and skin 104 of de-icer 100.
An ice cap 215 is deposited by an impinging airstream 219 and is shown
debonded and shattered into side ice-pieces 216 and 218, and nose ice
piece 217. The ice cap 215 is debonded and shattered by activation of the
skin deflection means 203 as discussed previously in relation to skin
deflection means 103 of de-icer 100. As before, tubes 207 and 211 are
provided to protect against shifts in the ice cap 215. De-icer 200 is
shown in an activated state by inflation of tube 210. Deflected profile of
skin 204 induced during subsequent inflation of tube 208 is shown as a
phantom line 212. Tube 210 is inflated by a pulse of compressed air which
forces the skin 204 to rapidly move outward. The motion of skin 204 during
inflation of tube 210 causes the ice cap 215 over tube 210 to debond and
shatter into ice-pieces 218 which are ejected into the airstream 219.
During subsequent inflation of tube 208, ice cap 215 debonds and shatters
over tube 208 and side ice-pieces 216 are ejected into the airstream 219.
Nose ice-piece 217 is located over the area where tubes 208 and 210 abut.
As shown, deflection of skin 204 over the edge of a tube is small in
comparison to the deflection over the center of a tube. Therefore,
activation of skin 204 over the apex 220 of de-icer 200 is much less than
activation of skin 104 over the apex 120 of de-icer 100. De-icer 100 is
generally more effective than de-icer 200 in removing ice over an apex.
However, depending on the radius of curvature over the apex, neither may
effectively remove ice.
Referring to de-icer 100 of FIG. 1 and de-icer 200 of FIG. 2, the radius of
curvature R over apexes 120 and 220, respectively, can have an adverse
effect on ice removal performance. De-icer 100A of FIG. 1A illustrates how
the geometry of the leading edge can effect ice removal performance.
De-icer 100A is shown attached to the substructure 102. Like numbered
components of de-icer 100 of FIG. 1 and de-icer 100A of FIG. 1A are
equivalent. A skin deflection means 103A is comprised of five tubes
107A-111A. Tubes 107-111 are identical to tubes 107A-111A except for the
width of each tube. The tube 109A overlying the apex 120 is wider than
tube 109. Tube 109A is shown inflated. Due to the position dependent
curvature of the outer surface 122, tube 109A tends to inflate on the
sides, where the radius of curvature is greater, away from the apex 120,
where the radius of curvature is lesser. Tube 109A has an outer wall 109A'
which is pulled down over the very tip of the apex 120 resulting in almost
no force application to the skin 104 over the tip of the apex 120.
Therefore, side ice-pieces 116 and 118 are removed, but nose ice-piece 117
located over the apex 120 is not removed. This phenomenon has been
observed in numerous icing wind tunnel tests.
Referring to de-icer 100 of FIG. 1, tube 109 also has an outer tube wall
109'. If the curvature of the apex 120 is not too great, and the width of
tube 109 is narrow enough, the outer tube wall 109' can deflect outward,
as shown in FIG. 1, and apply force to the skin 104 over the tip of the
apex 120 resulting in skin deflection 113. Ice piece 117 will be ejected.
De-icer 200 of FIG. 2 may provide a viable solution depending on geometry.
As a general guideline, de-icer 100 of FIG. 1 is suitable if the radius of
curvature R over apex 120 is greater than about 1.0 inch. In contrast,
de-icer 200 of FIG. 2 is suitable if the radius of curvature of apex 220
is between about 0.5 and 1.0 inch. However, de-icer 200 can be
unsatisfactory for use with leading edge geometries having a radius of
curvature R over apex 220 less than about 0.5 inch. A propeller blade
represents a type of leading edge geometry that often has an apex radius
of curvature of less that 0.5 inch. An effective means of removing ice
over an apex having a small radius of curvature is desired.
In addition to ice removal performance, life of a de-icer represents
another very important consideration. For the purposes of this
application, de-icer life is defined as the length of time a de-icer can
continuously operate before the de-icer mechanically fails. The components
of the de-icer are subjected to a stress cycle each time the de-icer is
activated. These stress cycles accumulate and eventually cause a de-icer
to mechanically fail due to fatigue. There are two ways to increase the
life of a de-icer similar to de-icers 100 or 200 without changing
materials. The cycle rate can be decreased (fewer cycles per minute), or
the stress levels can be reduced. Reducing the cycle rate usually is not
an option because flight conditions and ice accumulation characteristics
of an aircraft are usually fixed.
The other option, reducing the stress levels, is limited because skin
deflection in de-icers similar to de-icers 100 or 200 is achieved
predominantly by stretching the skin. Referring to de-icer 100 of FIG. 1,
the substructure 102 is relatively rigid and stretching the skin 104 is
the only way deflection of skin 104 over any of tubes 107-111 is achieved.
Referring to de-icer 200 of FIG. 2, this is also true of skin 204, tubes
207-211 and substructure 202. Referring to de-icer 100 of FIG. 1, a
maximum deflection 114 in skin 104 over tube 110 is presented. In general,
the maximum deflection 114 ranges between about 0.020 inch to about 0.060
inch. The maximum deflection 114 depends mostly on two variables; (1)
modulus of elasticity of the skin 104, and (2) the magnitude of force
generated by tube 110. For a given set of materials, the maximum
deflection 114 can be achieved only by increasing the force generated by
tube 114 to a sufficient magnitude. Increasing the force increases
stresses in tube 110 and skin 104 thereby decreasing life. Referring to
de-icer 200 of FIG. 2, the same is also true in relation to maximum
deflection 214 of skin 204 over tube 210 of de-icer 200. Therefore, a
means of obtaining a maximum deflection in a thin deflectable skin while
maintaining lower stresses in the skin and skin deflection means is
desired. Decreasing the stresses in the skin and skin deflection means
results in a de-icer having longer life.
In addition to ice removal, energy consumption and weight are also of
primary importance. De-icers similar to de-icers 100 and 200 have an
"active area." The term "active area" refers to that portion of the outer
skin that is dynamically activated by the thin force and displacement
generation means in a manner that removes ice accumulations. For example,
the active area of deicer 100 includes any area of skin 104 covering tubes
107-111 and the active area of de-icer 200 includes any area of skin 204
covering tubes 207-211. Normally, as evidenced by de-icers 100 and 200,
the surface area of the skin deflection means 103 and 203 must equal the
active area. Reducing the surface area of the skin deflection means
reduces the energy consumption of the de-icer. However, the active area
required for a particular application is usually fixed. Therefore, a way
of reducing the surface area of the skin deflection means without reducing
the active area is desired in order to provide a de-icer having decreased
energy consumption. Also, since the skin deflection means represent a
significant portion of the weight of a dynamic de-icer, reducing the
surface area of the skin deflection means in relation to the active area
should also reduce weight.
In the context of a pneumatic impulse embodiment, the force required to
deflect the outer skin bears on energy consumption and weight in a manner
that is even less apparent. For de-icers similar to de-icers 100 and 200
of FIGS. 1 and 2, the pulse propagation distance generally decreases as
the modulus of the skin increases. Pulse propagation distance refers to
the distance from a valve along the span of a tube over which ice is
effectively removed. In general, skin deflection and dynamics decrease
with distance from a valve because the pulse of compressed air is
constantly expanding and the peak pressure inside the tube decreases with
distance from the valve. For example, if the erosion layer 105 or 205 is
formed from 0.005 inch thick 15-3 titanium alloy, the pulse may generate
effective ice removal about two feet on either side of a valve. Therefore,
the distance between valves would be about four feet in order to provide
effective ice removal along the span of a tube. Four valves per tube would
be required for a sixteen foot span. For an ice protector having five
tubes, a total of twenty valves would be required. By increasing the pulse
propagation distance, the space-between valves can be increased.
Increasing the space between valves reduces the number of valves and the
total weight of the system. Reducing the number of valves also increases
the reliability of the system by reducing the number of mechanical
components. Therefore, means of increasing the pulse propagation distance
between valves is desired in order to increase reliability and decrease
energy consumption and weight.
The devices described above represent advancements over previous de-icing
systems. In spite of these advancements, means of improving ice removal
performance, life, reliability, weight, and energy consumption are of
continuing interest. In particular, a de-icer is desired exhibiting the
excellent ice removal performance typical of the devices described above
while having increased life, reduced weight, and reduced energy
consumption.
SUMMARY OF THE INVENTION
The invention comprises a dynamic mechanical de-icer adapted for attachment
to a substructure, the de-icer having an outer surface that meets and
breaks an impinging airstream when attached to the substructure, the
substructure having an apex corresponding to the portion of the de-icer
and substructure underlying the area of the outer surface where the radius
of curvature is smallest, comprising:
skin means for transferring tension from a first area of said skin means to
a second area of said skin means upon deflection of said first area away
from the substructure, said skin means overlying the substructure with
said first area spaced to one side of the apex and said second area at the
apex;
skin deflection means disposed beneath said skin means for deflecting said
deflectable skin away from the substructure; and
compressible means disposed beneath said skin means for permitting
deflection of said second area toward the substructure by compressing in
response to tension transferred by said skin means from said first area to
said second area upon deflection of said first area away from the
substructure.
According to an aspect of the invention, said compressible member divides
said skin deflection means, said compressible member being immediately
subjacent said skin, and said skin deflection means abuts said
compressible member.
According to another aspect of the invention, said skin deflection means
overlies said compressible member, said skin deflection means being
immediately subjacent said skin.
According to a further aspect of the invention, said thin deflectable skin
includes at least one layer of fiber reinforced plastic that selectively
stiffens said skin in a predetermined area.
According to a further aspect of the invention, the substructure has a
chordwise direction generally parallel to the direction of the impinging
airstream and a spanwise direction in which the substructure extends
generally perpendicular to the chordwise direction, and said skin
deflection means comprises at least two expandable tubes extending in the
spanwise direction, one each on either side of said compressible member,
each said tube abutting said compressible member.
According to a further aspect of the invention, said skin deflection means
comprises at least two expandable tubes extending in the spanwise
direction, said tubes abutting each other over said compressible member.
According to a further aspect of the invention, said skin deflection means
comprises at least three expandable tubes extending in the chordwise
direction, one tube overlying said compressible member, the other two
tubes being disposed on either side of and abutting said tube overlying
said compressible member.
According to a further aspect of the invention, said skin deflection means
comprises electromagnetic apparatus, said electromagnetic apparatus being
of the type that utilizes a high magnitude short duration current pulse to
develop opposing electromagnetic fields that cause said skin to be
deflected from the substructure.
According to a further aspect of the invention, said electromagnetic
apparatus includes at least one coil, said high magnitude short duration
current pulse being applied to each coil, each coil including:
a first, sheet-like member defined by a first, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said first conductor defining an electrical input and said
second end of said first conductor defining an electrical output;
a second, sheet-like member defined by a second, continuous, electrical
conductor having a plurality of turns and first and second ends, said
first end of said second conductor defining an electrical input, and said
second end of said second conductor defining an electrical output;
an electrical connection between said second end of said first conductor
and said first end of said second conductor; and
said first and second sheet-like members being disposed parallel to each
other with selected turns of said first electrical conductor being
positioned adjacent to selected turns of said second electrical conductor
such that said direction of current flow through the turns of said first
conductor is in the same direction as the current flow through the turns
of said second conductor.
According a further aspect of the invention, said electromagnetic apparatus
comprises at least two coils, one each on either side of said compressible
member, each coil abutting said compressible member.
According to a further aspect of the invention, said electromagnetic
apparatus comprises a target adjacent each coil, said target being
superposed over said coil, said coil being separable from said target, one
of the opposing electromagnetic fields being developed by said coil upon
application of said high magnitude short duration current pulse and the
other opposing electromagnetic field being developed in said target by
eddy currents induced by said coil electromagnetic field.
According to a further aspect of the invention, said electromagnetic
apparatus comprises at least two coils, said coils being adjacent each
other with one coil superposed over said other coil, said coils being
separable from each other, one of the opposing electromagnetic fields
being developed upon application of said high magnitude short duration
current pulse to one coil and the other opposing electromagnetic field
being developed upon application of said high magnitude short duration
current pulse to said other coil, said coils being electrically
interconnected such that current direction in said selected turns of said
conductor of one coil is opposite to said current direction in said
selected turns of said conductor of said other coil.
According to a still further aspect of the invention, said skin deflection
means includes electromagnetic apparatus, the electromagnetic apparatus
comprising at least two coils abutting each other along an edge overlying
the apex, said high magnitude short duration current pulse being applied
to each coil.
According to a further aspect of the invention, said skin deflection means
includes electromagnetic apparatus, said electromagnetic apparatus
comprising at least three coils, one coil overlying said compressible
member in between and abutting said other two coils, said high magnitude
short duration current pulse being applied to each coil.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary sectional view of a certain de-icer in the art
attached to a substructure;
FIG. 1A is a fragmentary sectional view of an alternate embodiment of the
de-icer depicted in FIG. 1;
FIG. 2 is a fragmentary sectional view of a certain de-icer in the art
attached to a substructure;
FIG. 3 is a fragmentary sectional view of a de-icer embodying the invention
attached to a substructure, depicted in the inactivated state;
FIG. 3A is a fragmentary sectional view of a de-icer embodying the
invention attached to a substructure, depicted in an activated state;
FIG. 3B is an isometric view of the de-icer of FIG. 3;
FIG. 3C is a fragmentary sectional view of an alternate embodiment of the
de-icer of FIG. 3B.
FIG. 3D is a fragmentary sectional view of an alternate embodiment of the
de-icer of FIG. 3B.
FIG. 4 is an isometric view of a de-icer incorporating electromagnetic
apparatus attached to a substructure.
FIG. 4A is a fragmentary sectional view of an alternate embodiment of the
de-icer of FIG. 4.
FIG. 4B is a fragmentary sectional view of an alternate embodiment of the
de-icer of FIG. 4.
FIG. 5 is an exploded isometric view of an electro-impulse embodiment for a
skin deflection means.
FIG. 6 is an exploded isometric view of an electro-repulsive embodiment for
a skin deflection means.
FIG. 7 is a fragmentary sectional view of a best mode de-icer for a low
speed general aviation aircraft.
FIG. 8 is a fragmentary isometric view of a best mode de-icer for a
propeller blade.
DETAILED DESCRIPTION
The invention comprises a new structure for a mechanical impulse de-icer
that changes the way in which the outer skin is deflected. Referring to
FIG. 3, a de-icer 300 embodying the invention is presented. A de-icer 300
is shown attached to a substructure 302. Centerline 321 bisects de-icer
300 and substructure 302. De-icer 300 and substructure 302 have a
chordwise and spanwise direction as previously discussed in relation to
de-icers 100 and 200 of FIGS. 1 and 2. De-icer 300 also has an apex 320. A
surrounding airflow 319 is shown impinging upon de-icer 300. An ice cap
315 is deposited by the airflow 319 during flight in atmospheric icing
conditions. The section shown in FIG. 3 is a chordwise cross-section.
De-icer 300 has an outer surface 322 the functions to meet and break the
impinging airstream 319. The outer surface 322 has a radius of curvature
R, measured perpendicular to the outer surface 322, that changes depending
on the chordwise position along the outer surface 322 as discussed
previously in relation to de-icers 100 and 200 of FIGS. 1 and 2.
De-icer 300 comprises a thin deflectable skin 304, skin deflection means
303, and a compressible member 323. In the embodiment presented, the skin
deflection means 303 comprises four expandable tubes 307-311. The tubes
are activated by sequentially releasing small quantities of compressed gas
into each tube as described by the Integral Expulsive System Patent, U.S.
Pat. No. 5,098,037, which is fully incorporated herein by reference. The
skin deflection means 303 can also take forms utilizing electromagnetic
apparatus. Examples are presented in the Electro-Impulse Patent, U.S. Pat.
No. 5,129,598 and the Planar Coil Patent U.S. Pat. No. 5,152,480 the
disclosures of which are fully incorporated herein by reference. Unless
noted otherwise, the discussion that follows relates with equal force to
dynamic de-icers that utilize skin deflection means comprising
electromagnetic apparatus.
In the embodiment presented, compressible member 323 divides the skin
deflection means 303. The skin deflection means 303 abut the compressible
member 323 which is immediately subjacent the skin. The substructure 302
provides the structural integrity necessary to absorb and resist flight
loads and unexpected impacts with foreign objects. The substructure can be
formed from a metal, such as aluminum, or fiber reinforced plastic
materials that are commonly used on aircraft such as epoxy impregnated
glass or graphite fabrics. The skin 304 includes a backing layer 306 and a
layer of erosion resistant material 305. The backing layer 306 can be
formed from fiber reinforced plastic material, such as nitrile phenolic or
epoxy impregnated into a fabric composed of fibers belonging to one of a
group including carbon fibers, glass fibers, and nylon fibers. The erosion
layer 305 can be formed from rubber, metal, or plastic, such as neoprene,
titanium foil, polyether-ether-ketone film, polyurethane film, and
polyurethane paint depending on the application. The erosion layer 305 is
necessary to provide resistance to impact from rain, sand, and other
debris that would damage the backing layer 306. The skin 304 and
compressible member 323 must have elastic properties. The term "elastic"
refers to the tendency of a material to return entirely to its rest state
within a short period of time after an imposed force is removed. Examples
of suitable materials for the compressible member include natural rubber,
and synthetic rubbers such as butyl or silicone rubber. The skin 304, skin
deflection means 303, and substructure 302 can be permanently bonded
together to form a unitary structure with integral ice removal capability
as described in the Integral Expulsive System Patent. Alternatively, the
skin 304 and skin deflection means 303 can combined into a unitary
structure which is then attached to an existing aircraft substructure 302.
In the embodiment presented, the skin deflection means 303 consists of four
expandable tubes 307-311. The expandable tubes 307-311 can be formed from
fiber reinforced plastic material such as nitrile phenolic coated nylon
fabric, or rubber coated fabric such as neoprene coated nylon fabric. The
de-icer 300 is activated by sequentially releasing small quantities of
compressed air into the tubes 307-311 as described in the Pneumatic
Impulse Patent or Integral Expulsive System Patent. Inflation of a tube is
preferably achieved in less than 0.1 second and most preferably in less
than 500 microseconds.
Referring now to FIG. 3A, de-icer 300 is shown in an activated state by
inflation of tube 310. Components having the same numbers in FIGS. 3 and
3A are equivalent. Tubes 307, 308 and 311 are shown not inflated. The rest
position of the skin 304 over the compressible member 323 is shown as a
dashed line 324. The deflected profile of skin 304 induced during
subsequent inflation of tube 308 is shown as a phantom line 312.
Rapid inflation of tube 310 deflects a first area of the skin 304 outward
developing tension in skin 304. The skin 304 transfers tension to a second
area of the skin 304 which compresses the compressible member 323,
allowing the second area of skin 304 over the compressible member 323 to
move inward. This movement must occur rapidly enough to debond and shatter
the ice cap 315 and eject the side ice-pieces 318 into the impinging
airstream 319 where they are swept away from the de-icer 300. The
compressed air is subsequently vented from tube 310, and the skin 304
snaps back to its rest position due to the elastic properties of the skin
304 and compressible member 323. The process is repeated by inflation of
tube 308 resulting in removal of side ice-pieces 316. The skin 304 over
the compressible member 323 moves inward upon inflation of any of the
tubes 307-311, thereby generating maximum compression 313.
A nose ice-piece 317 is removed during this sequence. Nose ice-piece 317
may be removed by two mechanisms. During the first part of the deflection,
skin 304 is rapidly accelerated inward away from the ice-piece 317. This
rapid acceleration may develop a gap between the skin 304 and the
ice-piece 317, or may move the ice-piece 317 just enough to allow the
airflow 319 to sweep the ice piece 317 away from the de-icer 300. However,
this movement may not be sufficient to remove ice-piece 317 and the
airstream 319 may force the ice-piece 317 to move inward with the skin
304. During the second part of the deflection, skin 304 may eject the
ice-piece 317 into airstream 319 when it snaps back to its rest position
324. Regardless of the exact mechanism responsible for ice removal, the
invention has been found to be very effective in removing ice over the
apex 320. Also, ice removal over the apex 320 is enhanced since the skin
304 over the compressible member 323 is deflected each time one of the
tubes 307-311 is inflated.
By comparing de-icer 300 with de-icer 100 of FIG. 1 and de-icer 200 of FIG.
2, a principal advantage of the invention can now be appreciated. As
discussed previously, the energy consumption of a dynamic mechanical
de-icer is proportional to the surface area of the skin deflection means
303 immediately subjacent the skin 304. Referring to de-icer 300, the
surface area of the skin deflection means 303 is less than the active
area. The area over the compressible member makes up the difference.
Therefore, de-icer 300 consumes less energy than de-icers 100 or 200.
Reducing the surface area of the skin deflection means 303 also reduces
weight because the materials that form the skin deflection means 303 are
generally more massive than the materials that form the compressible
member 323.
In addition to reducing energy consumption and weight, the invention also
improves the life of a dynamic de-icer. As discussed previously, achieving
deflection in the skin of a deicer similar to de-icers 100 or 200 of FIGS.
1 and 2 can only be achieved by stretching the skin. In contrast, de-icer
300 of FIG. 1 achieves deflection of the skin 304 by two mechanisms; (1)
stretching the skin 304, and (2) compressing the compressible member 323.
Referring now to de-icer 300 of FIG. 3A, a certain maximum deflection 314
is necessary in order to achieve ice removal. The maximum deflection 314
depends on the materials and application, but generally ranges from 0.020
inch to 0.060 inch. The maximum deflection 314 of skin 304 over tube 310
is directly related to the maximum compression 313 of the compressible
member 323. Decreasing the modulus of elasticity of the compressible
member 323 increases maximum compression 313 and the maximum deflection
314 for a fixed level of force generation in the skin deflection means
303. Looking at the relationship another way, decreasing the modulus of
elasticity of the compressible member 323 decreases the level of force
generation in the skin deflection means 303 necessary to achieve a certain
maximum deflection 314. The level of force generation in the skin
deflection means 303 can be reduced, while still maintaining the maximum
deflection 314, by choosing a material with an appropriate modulus of
elasticity for the compressible member 323. Reducing the level of force
generation in the skin deflection means 303 decreases the tension in skin
304. Stress in the skin deflection means 303 is reduced by decreasing the
level of force generation. Likewise, stress in the skin 304 is reduced by
reducing the level of tension. Therefore, the invention provides a means
of reducing the stress levels in the components of a dynamic de-icer. As
discussed previously, reducing the stress levels increases life. The
superior life resulting from the invention has been demonstrated in
several bench tests.
The decreased tension in skin 304 required to obtain a desired deflection
also improves energy consumption and weight. As mentioned previously, the
invention decreases stress in skin 304 and permits decreased force
generation in the skin deflection means 303. Since less force is required,
less material is required to absorb and distribute reaction forces from
the skin deflection means 303. The substructure 302, skin deflection means
303, and skin 304 can all be lighter in weight since the invention reduces
the force each must withstand.
Since less force is required to deflect the skin 304, less energy is
required to generate that force. For skin deflection means utilizing
expandable tubes, lower peak tube pressures are required which decreases
valve supply pressure. Lower supply pressure results in a lighter valve
and solenoid, lighter supply lines and a lighter compressor. For thin
force and displacement generation means utilizing electromechanical
apparatus, the supply voltage and resulting current can be decreased.
Decreasing the voltage and current requirements results in lighter supply
lines, lighter switching hardware, and lighter energy storage devices.
Additional weight and energy savings are gained in a pneumatic impulse ice
protector embodiment. Pneumatic impulse valves, of the type described in
U.S. Pat. No. 4,878,647 PNEUMATIC IMPULSE VALVE AND SEPARATION SYSTEM,
Putt et al., are spaced along the spanwise length of a expandable tube
(pneumatic impulse tube). The distance between valves depends on the pulse
propagation distance as previously discussed in relation to de-icers 100
and 200 of FIGS. 1 and 2. The pulse propagation distance of a de-icer
similar to de-icers 100 or 200 is limited by the stiffness of the outer
skin. The pulse propagation distance of de-icer 300 is greater because the
skin 304 of de-icer 300 is easier to deflect. For example, if skin 304 is
formed from 0.005 inch thick 15-3 titanium alloy, the pulse may generate
effective ice removal about four feet on either side of a valve.
Therefore, the distance between valves must be about eight feet in order
to provide effective ice removal along the span of a tube. Two valves per
tube would be required for a sixteen foot span. For an ice protector
having a compressible member and five tubes, a total of only ten valves
would be required. However, de-icer 300 presents a further advantage since
its active area is the same as the active area of de-icer 100, but de-icer
300 has only four tubes. In other words, de-icer 300 would require only
eight valves compared to the sixteen valves required by de-icer 100. In
this hypothetical example, the number of valves has been reduced by
one-half. Reducing the number of valves reduces energy consumption,
weight, cost, and complexity of the system. Fewer valves also increases
the reliability because the resulting system has many fewer mechanical
components.
The invention also produces improvements in ice removal performance. In
general, the ice removal performance of a dynamic de-icer is strongly
related to how quickly the outer skin moves. As the movement rate of the
surface increases, minimum ice removal thickness decreases along with the
quantity of residual ice left after ice cap removal. In general, a surface
frequency response of at least 2000 hertz and a deflection of at least
0.020 inches and a peak acceleration of at least 3000 g (1 g=32.2 f/s
.sup.2) is desirable. This application is filed in conjunction with
copending and co-owned application Ser. No. 07/998,360 IMPROVED SKIN FOR A
DE-ICER, Rauckhorst et al., filed Dec. 30, 1992, which is herein
incorporated by reference (hereinafter referred to as the Improved Skin
Application).
In general, the dynamic frequency response of a thin deflectable skin is
increased by increasing its modulus of elasticity. Materials having an
elevated modulus of elasticity and a tendency to transmit rather than damp
dynamic motion are preferred. For the purposes of this application, an
"elevated modulus" means a modulus of elasticity greater than 40,000 kPa.
Examples of desirable materials for the backing layer 306 include but are
not limited to fiber reinforced plastics which are preferred over natural
or synthetic rubbers. Fiberglass or carbon fiber reinforced nitrile
phenolic or epoxy are particularly useful. Materials having less of a
tendency to absorb and damp dynamic movement are also desirable in order
to minimize the amount of impulse energy absorbed by the backing layer
306. As much of the impulse energy as possible should be transmitted to
the ice layer. Kevlar.RTM. (aramid fiber) generally is not desirable
because of its tendency to absorb and damp the dynamic motion induced by
the skin deflection means.
As a part of the skin, mechanical properties of the layer of erosion
resistant material also perform an important role in the ice removal
performance of dynamic de-icers. In particular, materials having an
elevated modulus of elasticity and a tendency to transmit rather than damp
dynamic motion exhibit the best ice removal properties. Examples of such
materials include plastic films, such as polyurethane or
polyether-ether-ketone and metal foils such as titanium, aluminum, or
stainless steel. These materials generally perform better than low modulus
materials such as natural or synthetic rubber, and polyurethane elastomer.
These materials exhibit better ice removal performance for two reasons.
First, they generally have less of a tendency to absorb and damp the
dynamic motion induced by the skin deflection means. Dynamic energy tends
to be absorbed and dissipated in a low modulus erosion layer rather than
being efficiently transmitted to the ice layer. Second, ice removal is
partially achieved by changing the surface curvature to develop shear
stresses along the adhesion line at the interface of the ice cap and the
erosion layer. These shear stresses contribute to destroying the adhesion
along the interface, thereby releasing the ice cap to be ejected from the
de-icer surface. Low modulus materials tend to distribute and dissipate
the shear stresses along the interface. Elevated modulus materials tend to
concentrate shear stresses along the interface. Examples of suitable
materials include metal foils, such as titanium, or plastic films, such as
polyether-ether-ketone or polyurethane. Because of these effects, a
de-icer with a low modulus surface generally leaves more residual ice, and
cannot remove thicknesses of ice as thin as a de-icer having an elevated
modulus surface.
Another important advantage of the invention can now be appreciated. The
preceding discussion emphasizes that, for the best ice removal
performance, the skin materials should be selected from a group of
materials having an elevated modulus and a tendency to transmit rather
than damp dynamic motion. As discussed previously, deflection of a high
modulus skin requires more force with a de-icer similar to de-icers 100 or
200 than with a de-icer similar to de-icer 300 having a compressible
member 323. Decreasing the force increases the life of a dynamic de-icer.
Therefore, de-icer 300 permits use of an elevated modulus skin 304, and
the attendant ice removal performance, while maintaining lower stress
levels and a longer life.
Though not fully explored, the compressible member 323 also effects the
dynamic response of the skin 304. The damping qualities of some materials
may prove to be undesirable. Increasing the modulus of the compressible
member material should increase the frequency response of the skin 304.
However, increasing the modulus also increases the force required to
achieve a desired deflection of skin 304 which affects life. Life and ice
removal performance must always be balanced. The upper limit for the
durometer of the compressible member should be about a Shore D 70, but
preferably less than Shore A 90. A strip of chlorobutyl rubber having a
Shore A durometer within the range from about 55 to 65 is particularly
useful, especially when combined with a carbon or glass fiber reinforced
nitrile phenolic skin 304. An outer skin of fabric reinforced Neoprene is
also useful in combination with a butyl rubber compressible member. The
width of the compressible member 323 depends on the application, but would
probably fall between 1/4 inch and 2 inches for most applications. The
thickness is preferably less than 0.100 inch and a thickness as low as
0.050 inch may prove satisfactory for many applications. A thinner
compressible member is preferable because it weighs less and is easier to
manufacture.
As discussed previously, ice removal over the apex of de-icers 100 and 200
may prove unsatisfactory depending on the geometry. Specifically, removing
ice over an apex from a surface having a radius of curvature less than
0.50 inch can be difficult. Removing ice over an apex having a radius of
curvature less than 0.25 inch is particularly difficult. As evidenced by
de-icer 300, the invention provides a means whereby the ice removal over
an apex is improved. The increased action in skin 304 over the
compressible member 323 greatly improves ice removal over the apex, which
is especially useful with surface geometries having a small radius of
curvature.
Referring now to FIGS. 3B through 3D, different tube and compressible
member arrangements are presented and may be desirable depending on the
application. Like numbered components in FIGS. 3 through 3D are
equivalent. Referring to de-icer 300 of FIG. 3, the skin deflection means
303 are divided by the compressible member 323 and overly the substructure
extending from either side of the apex 320. Tubes 307 and 308 overlie the
substructure 302 abutting each other along one edge. One edge of tube 308
abuts the compressible member 323. Tubes 310 and 311 are arranged
similarly overlying the opposing portion of the substructure 302. Tubes
307-311 extend in the spanwise direction beneath the skin 304.
Referring to FIG. 3C, de-icer 300C has skin deflection means 303C composed
of tubes 307C-311C. Here, the skin deflection means 303C overlie the
compressible member 323. Tube 309C overlies the compressible member 323
and tubes 307C and 308C overly the substructure abutting each other along
one edge. Tube 308C abuts tube 309C along one edge. Tubes 310C and 311C
are similarly arranged overlying the opposing portion of substructure 302.
Tubes 307C-311C extend in the spanwise direction beneath the skin 304.
This arrangement may be useful if ice removal over the apex 323 is not
entirely satisfactory with de-icer 300 of FIG. 3B. De-icer 300C will
probably consume more energy than de-icer 300 because the skin deflection
means 303C have a larger surface area than skin deflection means 303.
However, other advantages of the invention relating to energy consumption,
weight, cost and reliability can still be realized.
Tube 309C could also be positioned between the substructure 302 and the
compressible member 323. The compressible member 323 would then be in
direct contact with the skin 304. This arrangement (not shown) is believed
to be less desirable because dynamic motion induced by tube 309C would
pass through the compressible member 323 before reaching the skin 304. The
compressible member 323 would probably absorb much of the dynamic motion
before reaching the skin 304 resulting in decreased ice removal
effectiveness.
In FIG. 3D, de-icer 300D represents another arrangement where the skin
deflection means overlie the apex. Skin deflection means 303D is comprised
of expandable tubes 307D-311D. Tubes 308D and 310D abut along one edge
directly over the apex 320. Tubes 307D and 308D abut each other along one
edge. Tubes 311D and 310D are similarly arranged overlying the opposing
portion of the substructure 302. Tubes 307D-311D extend in the spanwise
direction beneath the skin 304. This arrangement may also be desirable if
ice removal performance of de-icer 300 of FIG. 3B is not entirely
satisfactory. De-icer 300D will probably consume more energy than de-icer
300 because the skin deflection means have a larger surface area. Once
again, however, other advantages of the invention relating to energy
consumption, weight, cost and reliability can still be realized.
The best tube and compressible member arrangement depends on a variety of
factors that can vary greatly depending on an airframe manufacturer's
specifications. Such factors include, the leading edge geometry, flight
characteristics, maximum thickness of ice that can be tolerated, cost,
life, reliability and weight. An arrangement similar to de-icer 300 is
most desirable. However, depending on the application, ice removal
performance over the apex may require use of arrangements similar to
de-icers 300C or 300D. Optimizing the design is a process that iterates
between bench testing and icing wind tunnel testing. Life tests, rain
erosion tests, dynamic tests and icing wind tunnel tests are cyclically
performed with an eye toward improving each property. Changing the design
to improve one of these factors may have an adverse effect on another. The
rain erosion test parameters described in the Integrated Pneumatic Impulse
Patent are particularly useful for determining rain erosion
characteristics. Dynamic tests can be considered as a subset of icing wind
tunnel tests since improving skin dynamics usually improves ice removal
performance. A Polytech Model No. OFV 300 laser vibrometer system has been
found to be very effective for bench testing designs in order to determine
dynamic displacements, velocities, and accelerations at various locations
on the skin. In general, a peak skin acceleration of at least 3000 g's (1
g=32.2 f/sec.sup.2) at a peak frequency of at least 2000 hertz with a peak
deflection of 0.020 inch is desirable. Much greater accelerations may be
necessary depending on ice removal requirements.
FIGS. 4 through 4B present similar arrangements, but the thin skin
deflection means incorporate electromagnetic apparatus. Examples of two
types of electromagnetic apparatus that can be employed as skin deflection
means are presented in FIGS. 5 and 6. These are intended to be viewed only
as examples of the different types of skin deflection means that can be
used in combination with the claimed invention. The types of structures
that can be used in the practice of the claimed invention are not limited
to the examples shown.
The electromagnetic apparatus of FIG. 5 comprises an eddy current
separation assembly 550. Eddy current separation assembly 550 includes a
planar coil 551, an upper dielectric layer 556, a coil dielectric layer
557, a target dielectric layer 558, a target 559, and a lower dielectric
layer 560. The planar coil 551 includes two coil members 553 and 554
disposed on the opposite sides of a dielectric carrier 552. The coil
members 553 and 554 are mirror images of each other as described in the
Planar Coil Patent. An electrical connection 555 is provided at the center
which electrically connects the two coils. A small copper rivet has been
found useful in forming electrical connection 555, but a weld is more
preferable. The coil members 553 and 554 are most preferably formed from
etched copper foil, but other materials may be used as described in the
Planar Coil Patent. The dielectric carrier 552 can be formed from any
material having good mechanical and dielectric properties such as
plastics, fiber reinforced plastics, and synthetic rubbers.
Planar coil 551 is encapsulated between upper dielectric layer 556 and coil
dielectric layer 557. The target 559 is encapsulated between target
dielectric layer 558 and lower dielectric layer 560. The upper dielectric
layer 556, coil 551, and coil dielectric layer 557 together form an upper
member indicated by the letter U. The lower dielectric layer 560, target
559, and target dielectric layer 558 together form a lower member
indicated by the letter L. The upper member U and lower member L are
joined along an upper bond perimeter 562 and lower bond perimeter 561
forming a assembly.
The target 559 is superposed next to the coil 551. Electrical leads (not
shown) are attached to the coil members 553 and 554 and are also
encapsulated between upper and lower dielectric layers 556 and 560. Target
559 is formed from conductive material such as copper or aluminum sheet.
The various dielectric layers are formed from materials having good
dielectric and mechanical properties. Examples of such materials are
plastics, reinforced plastics, and synthetic rubbers.
Upon application of a large magnitude transient potential to the coil 551,
a large magnitude transient current is generated in the coil and eddy
currents are formed in the target 559. The upper member U is forcefully
repulsed from the lower member L. The upper member U is not bonded to the
lower member L in the area between the coil 551 and target 559 thereby
permitting movement. The active area is roughly defined by the area of the
target 559 or planar coil 551. Apparatus for achieving a shaped large
magnitude current pulse is presented in the Planar Coil Patent.
The electromagnetic apparatus of FIG. 6 comprises electro-repulsive
separation assembly 650. Upper coil 651 is composed of two coil members
653 and 654 disposed on opposite sides of a dielectric carrier 652. The
coil members 653 and 654 are arranged the same as coil members 553 and 554
of planar coil 551. Electrical connection 655 connects the ends of the
coil member 654 and 653 through the dielectric layer at the center. Lower
planar coil 656 is composed of two coil members 658 and 659 disposed on
opposite sides of a dielectric carrier 657. Planar coil 656 is identical
to planar coil 651. Electrical connection 660 connects the ends of the
coil members 658 and 659 through the dielectric layer at the center. A
small copper rivet has been found to be useful for this purpose, but a
weld is preferred.
Upper planar coil 651 is encapsulated in an upper dielectric layer 661 and
an upper coil dielectric layer 662 thereby forming an upper member U.
Lower planar coil is encapsulated in a lower dielectric layer 664 and
lower coil dielectric layer 663 thereby forming a lower member L. The
upper and lower members U and L are joined at the upper and lower bond
perimeters 665 and 666 which forms the separation assembly 650. The upper
coil 651 is superposed over the lower coil 651 such that the conductors in
each are substantially aligned. The upper member U and lower member L are
not bonded together in the area between the coils 651 and 656. An
electrical connection 667 is formed between the ribbon lead extending from
coil member 653 and the ribbon lead extending from coil member 658. The
connection is shown as a dashed line because FIG. 6 is an exploded view
and the ribbon leads are actually adjacent to each other. Separate
electrical leads (not shown) are electrically connected (not shown) to an
upper coil lead 668 and a lower coil lead 669. The electrical connections
are encapsulated in the upper and lower dielectric layers 661 and 664.
During operation, a high magnitude transient potential is applied across
the leads 668 and 669. The potential induces a high magnitude transient
current, in the coils 651 and 656. The current direction in any conductor
of the upper coil members 653 or 654 will be substantially opposite to the
current direction in the adjacent conductor of the lower coil members 658
or 659. Because the current direction is opposite, the upper coil members
653 and 654 forcefully repel the lower coil members 658 and 659. The upper
member U is thereby forcefully repelled and displaced from the lower
member L. The active area of the separation assembly is defined by the
area of the planar coils 651 and 656.
The coils depicted in FIGS. 5 and 6 have been referred to as "planar"
coils. The term "planar" is intended to refer only to the thin sheet-like
qualities of the coil as described in the planar coil patent. The coils
depicted in FIGS. 5 and 6 could be formed to a curved surface if they are
constructed of sufficiently flexible materials. If the materials are not
sufficiently flexible, the coils could be cured to shape under heat and
pressure in a mold or press.
Returning now to FIGS. 4 through 4B, various arrangements are presented
that use skin deflection means comprising electromagnetic apparatus,
wherein like numbered components are equivalent. The electro-repulsive
separation assembly 650 and eddy current separation assembly 550 are
examples of such apparatus. Since the active area of any separation
assembly is roughly defined by the area of the coil, several separation
assemblies must be disposed spaced along the span of the de-icer. The
active area of each separation assembly roughly defines a segment.
In FIG. 4, a de-icer 400 is shown attached to a substructure 402. De-icer
400 is comprised of a skin 404, skin deflection means 403, and a
compressible member 423. The substructure 402 and de-icer have an apex 420
and are bisected by a centerline 421. The skin deflection means 403 of
de-icer 400 is comprised of several separation assemblies spaced along the
span of de-icer 400 underlying the skin 404. This feature is different
than previous embodiments using expandable tubes because tubes can easily
run the length of a span whereas coils are more confined in their extent.
Larger coils inherently have a larger electrical resistance which results
lower peak current and lower separation force. The active area of each
separation assembly is defined by segments 424-427. Segments are similarly
defined overlying the opposing portion of substructure 402 which are not
in view as presented in FIG. 4. Separation assemblies 407-411 are spaced
around the substructure 402 in the chordwise direction. Separation
assemblies 411 and 410 abut along one edge of each separation assembly.
Separation assembly 410 (and the coil within) abuts the compressible
member 423 along one edge. Separation assemblies 407 and 408 are similarly
arranged overlying the opposing portion of substructure 402.
In operation, a high magnitude current pulse is applied sequentially to the
leads of each separation assembly. As previously discussed, the upper
member U and lower member L, as shown in FIGS. 5 and 6, are forcefully
repelled away from each other. The substructure 402 resists the reaction
from one of the members. The other member forces the skin 404 away from
the substructure 402. The resulting deflection of the skin 404 is quite
similar to that presented in FIG. 3A. This action can be induced by either
an eddy current separation assembly 550 or an electro-repulsive separation
assembly 650.
Another arrangement is presented in FIG. 4A. De-icer 400A is attached to
substructure 402. De-icer 400 is comprised of skin 404, skin deflection
means 403A and compressible member 423. Skin deflection means 403A are
similar to skin deflection means 403 except an additional separation
assembly 409A overlies the apex 420. Separation assemblies 407A and 408A
abut along one edge of each separation assembly. Separation assembly 408A
abuts separation assembly 409A along one edge of each separation assembly.
Separation assemblies 410A and 411A are similarly arranged overlying the
opposing portion of substructure 402. Other separation assemblies (not
shown) are distributed in the spanwise direction underlying the skin 404
forming segments (not shown) similar to de-icer 400. This arrangement may
be desirable if ice removal over the apex 423 of de-icer 400 is not
satisfactory. Separation assembly 409A could be placed beneath the
compressible member 423, but this would probably result in less effective
ice removal.
Another arrangement is presented in FIG. 4B. De-icer 400B is attached to
substructure 402. De-icer 400B is comprised of skin 404, skin deflection
means 403B, and compressible member 423. Skin deflection means 403B is
similar to skin deflection means 403 except separation assemblies 408B and
410B abut each other along one edge over the compressible member 423.
Separation assembly 407B abuts separation assembly 408B along one edge.
Likewise, separation assembly 410B abuts separation assembly 411B along
one edge. As before, additional separation assemblies (not shown) are
distributed in the spanwise direction which form several segments (not
shown). De-icer 400B is another example of an arrangement that may be used
if ice removal over the apex 423 of de-icer 400 is unsatisfactory.
Though discussed in terms of individual separation assemblies, comparing
FIGS. 5 and 6 with FIGS. 4 through 4B suggests that several separation
assemblies could be formed into a single unitary blanket. For example, the
four separation assemblies underlying the four segments of de-icer 400 as
shown in FIG. 4 could be combined into a single blanket. Referring to FIG.
5, four coils could be distributed in side-by-side relationship between a
single upper dielectric layer 556 and single coil dielectric layer 557. A
single target 559 large enough to underlie all four coils 551 could be
encapsulated between a single lower dielectric layer 560 and target
dielectric layer 558. If this were done, the bond perimeters 562 and 561
would run around the perimeter defined by all four elements. The same
applies to FIG. 6. Four sets of planar coils 651 and 656 could be
distributed in side-by-side relationship between the upper dielectric
layer 661 and lower dielectric layer 664 thereby forming a single unitary
blanket. In either case, the segments 424-427 of de-icer 400 would still
be defined by the active area of each coil within each separation
assembly.
Other variations not specifically presented are also considered to be
within the purview of this invention. For example, the target 559 of FIG.
5 may not be required if the substructure is sufficiently conductive. In
this case, the thin force and displacement generation means would
constitute only the upper member U of FIG. 5. Several upper members could
be consolidated into a single blanket as discussed above. Also, the
compressible member has consistently been shown centered on the apex. It
could be shifted away from the apex in the chordwise direction as long as
a portion of the compressible member still overlies the apex. Shifting the
compressible member may be desirable depending on the geometry. Referring
to FIGS. 3D and 4B, the pneumatic tubes or separation assemblies abut over
the apex along the centerline. The edge along which they abut could be
shifted to one side of the centerline. Finally, in all of the embodiments
disclosed thus far, the active area has been symmetric with respect to the
centerline. Depending on the application, the active area could be shifted
so that active area overlying one portion of the substructure is greater
than the active area overlying the opposing portion. Also, the geometry of
the substructure and de-icer has been depicted as symmetric about the
centerline. In most applications, the active area and leading edge
geometry will not be symmetric about the centerline.
BEST MODE
A preferred mode of practicing the invention is presented in FIG. 7. This
mode is preferred for use on the fixed leading edge surfaces of a
relatively low speed (250 Knot max flight speed) aircraft, particularly
the leading edges of the wing, horizontal stabilizer, and vertical
stabilizer. A De-icer 750 and a substructure 751 are permanently bonded
together and are shown attached to an aircraft structure 97 by fasteners
96. De-icer 750 and substructure 751 have an apex 720 and are bisected by
a centerline 721.
A deflectable skin 752 is composed of an erosion layer 753 and a backing
layer 754. The backing layer 754 is selectively stiffened as described in
the Improved Skin Application. Three tubes 757, 758 and 759 extend in the
spanwise direction beneath the skin 752. Tube 759 on the upper surface
abuts the compressible member 762 along one edge and tube 758 abuts the
compressible member 762 along one edge. A marginal member along each edge
of tubes 757 and 758 form an overlap 760 as described in copending
application Ser. No. 07/832,472 AIRFOIL WITH INTEGRAL DE-ICER USING
OVERLAPPED TUBES, Rauckhorst et al. which is fully incorporated herein by
reference. The skin 752 is joined to the substructure 751 by peel tabs 755
and 756 which are folded over extensions of a tube assembly back ply 763.
Release layer 761 extends from the upper peel tab 755 to the lower peel
tab 756. The release layer 761 forms an unbonded member between the skin
752 and underlying tubes 757, 758 and 759 and compressible member 762.
Matching male and female tools are required to build de-icer 750. The
process begins by fabricating the backing layer 754. The male tool is
treated with release and a single layer of 3M AF32 nitrile phenolic film
adhesive is applied to the surface of tool. A layer of dry Ceiba-Geigy
CGG300 graphite fabric is then laid over the tool and manually conformed
to the shape of the tool. The fabric should be placed on an angle in
relation to the chordwise direction of the tool. An angle of 45.degree. is
preferred but may not be possible unless the fabric prewoven at an angle
of 45.degree. relative to width. A single coat of BFGoodrich A-626-B is
then applied which saturates and adheres the graphite fabric to the film
adhesive. The graphite fabric is then covered with a layer of perforated
release film which is conformed to the shape of the tool with no wrinkles.
A preferable film is catalogue number A-5000 P3 (holes on 1/2 inch
centers) produced by Richmond Aircraft Products, Inc. A vacuum bag is then
applied and vacuum is applied for a minimum of 120 hours which impregnates
the film adhesive into the graphite fabric. Following vacuum treatment,
the vacuum bag and release film are removed and the impregnated graphite
fabric is dried in open air for a minimum of 48 hours.
Following the drying period, the impregnated graphite fabric is removed
from the male tool, placed in the female tool, and cured under vacuum at
350.degree. F. under 70 psig pressure for a period of 30 minutes, thereby
forming a partially cured outer skin. After cure, a strip of teflon tape,
adherent on one side, is applied to the nose area of the skin that will
overly the compressible member 762. The tape is necessary to prevent epoxy
saturation of the outer skin overlying the compressible member 762. The
backing layer 754 is then selectively reinforced by applying a sheet of
Ceiba-Geigy R6376/CGG108 epoxy impregnated graphite fabric to the inside
surface of the outer skin from the edge of the tape to the trailing edge.
Two sheets are applied, one corresponding to the inside of the upper
surface and one corresponding to the inside of the lower surface of the
outer skin. Further sheets of R6376/CGG108 are applied over areas
corresponding to the valve inlet ports. Each sheet is about 12 inches wide
and 1 inch narrower in width than the side sheets already applied and is
shifted back one inch from the edge of the tape. A vacuum bag is then
applied. The selectively reinforced backing layer 754 is cured under
vacuum at 350.degree. F. and 50 psig for 60 minutes.
The impulse tubes are formed from tightly woven nylon fabric impregnated
with nitrile phenolic resin by the following process. A layer of AF32 film
adhesive is applied to a release film. A preferable release film is
catalogue no. Style 02232 Teflon coated fiberglass fabric produced by
Furon-CHR Division. A layer of nylon fabric is laid over the film
adhesive. A coat of A-626-B primer is applied which saturates and adheres
the fabric to the film adhesive. Another layer of release film is applied
over the fabric followed by a vacuum bag. Vacuum is applied at room
temperature for a period of 120 hours. The impregnated fabric is removed
from the vacuum bag and dried for 48 hours. It is important to note that
this process can be used to impregnate AF32 into nearly any type of
fabric.
Tube width usually ranges from 1/2 inch to 2 inches. Strips are cut from
the impregnated fabric wide enough to form a tube to provide for a full
width overlap (the width of the strip would be roughly three times the
finished width of the tube). The fabric is most preferably cut on an angle
in relation to the spanwise length of the tube. The preferred angle is
45.degree. but may not be attainable depending on tube length unless a
fabric is used that is prewoven on an angle of 45.degree. in relation to
its width. The fabric strip is placed on a flat surface with the coated
side facing up. A strip of Teflon tape adherent on one side, preferably 3M
204/3 tape, with a width corresponding to the inside width of the finished
tube is applied to the fabric strip. A billet, for example 0.030 inch
thick Teflon plastic, with a width corresponding to the finished width of
a tube is centered over the tape. The strip is then wrapped around the
billet in a widthwise direction forming a lengthwise extending overlapped
member corresponding to the width of the tube. The A-626-B primer can be
used for tack. An additional strip is preferably wrapped around the first
strip in the same manner forming a tube with a double thickness of
material (quadruple thickness in the overlap area). Three tubes 757, 758
and 759 are formed by this process.
A tube matt is then assembled on the male tool. The process begins by
applying a single layer of AF32 film adhesive to the surface of the tool.
A layer of tightly woven nylon fabric is draped over the tool and manually
conformed to its shape. A coat of A-626-B primer is applied that saturates
and adheres the fabric to the layer of film adhesive. A layer of
perforated release film is subsequently applied without wrinkles. After
application of a vacuum bag, vacuum is continuously applied for at least
120 hours at room temperature thereby impregnating the film adhesive into
the fabric. Following removal of the vacuum bag, the impregnated fabric is
permitted to dry at room temperature for a period of at least 48 hours.
This layer of impregnated fabric forms the back ply 763.
A strip of chlorobutyl rubber, cured to conform to the shape of the apex
and trimmed to final width, is applied to the back ply 763 overlying the
apex of the tool (corresponding to the apex 98 of the leading edge 99).
The butyl rubber preferably has a Shore A durometer in a range between
about 55 and 65. Tubes are similarly applied to the back ply 763 in the
appropriate locations. The tube overlap 760, about 0.25 inch, is formed at
this time. The release layer 761 is formed by applying teflon tape,
preferably 3M 204/3 tape adherent on one side, over the assembled tube
matt. The release layer 761 defines the extent of the unbonded area
between the tube matt and skin 752. The back ply 763 is subsequently
trimmed to within one inch of the edge of the release layer 761. The one
inch tab of the back ply 763 is then folded up and over to form the upper
peel tab 755 and lower peel tab 756. The entire assembly is then removed
from the male tool and placed in the female tool with the release layer
761 against the surface of the tool. A vacuum bag is applied and the tube
assembly is cured at 350.degree. F. under 50 psig pressure for 30 minutes.
After cure, the tube assembly is removed from the female tool. Apertures
are formed in the tubes for inlet valve fittings and exhaust ports. The
valve fittings are located intermediate the ends of the tubes in numbers
and locations sufficient to insure adequate ice removal. Each tube
normally has two exhaust ports, one located at each end. The fittings are
applied in the appropriate locations and additional nitrile phenolic
impregnated fabric patches are applied for reinforcement. The tube
assembly is then subjected to another cure in the female tool under vacuum
at 350.degree. and 50 psig for 30 minutes. The billets are then removed
and the tube ends are closed using a diaper closure. The tube assembly is
subjected to a third cure in the female tool under vacuum at 350.degree.
F. and 50 psig for 30 minutes.
After removing the tube assembly from the female tool, the completed skin
752 is inserted into the tool. Two one inch wide strips of Hysol EA-951
film adhesive are cut to the spanwise length of the upper peel tab 755 and
lower peel tab 356. The strips are tacked to the peel tabs 755 and 756
using Hysol EA-952 primer. The tube assembly is then placed inside the
skin 752 with the release layer 761 adjacent the inside surface of the
skin 752 and taped in place. A vacuum bag is applied and the assembly is
cured at 350.degree. and 50 psig pressure for 60 minutes.
A plurality of epoxy impregnated fabric reinforcement plies are applied to
the inside surface of the skin 752 and back ply 763 after removal from the
female tool. The type of reinforcement ply depends on the aircraft
manufacturer's specifications. For low speed aircraft, Ceiby-Geigy
913/CGG104 impregnated graphite fabric is suitable. The number of plies
and their orientations is subject to aircraft manufacturer specifications
and can be determined by those skilled in the art of composite material
design and fabrication. At least three plies are recommended with at least
one ply on a 45.degree. angle relative to the chordwise direction. The
plies must be cut and arranged to accommodate the valve fittings and
vacuum ports. The assembly is subjected to a final cure in the female tool
according to the reinforcement ply manufacturer's instructions.
After final cure, the part is trimmed to final dimensions. The erosion
layer 753 consists of a polyurethane paint and is applied to the finished
part either on a bench or after installment on an aircraft. Paint
conforming to MIL-Z-83826 applied by spray is preferred.
The preferred mode of practicing the invention can vary depending on the
application. Accordingly, a preferred embodiment for a propeller blade is
presented in FIG. 8. A de-icer 850 is shown attached to a propeller blade
863. De-icer 850 is formed in a thin sheet that is subsequently attached
to the propeller blade 863 by removable adhesive. The propeller blade 863
can be formed from metal or a fiber reinforced plastic composite and has
an apex 820. Though not shown, propeller blade 863 can be recessed to
accept de-icer 850 in which case the desired external shape of the
propeller 863 is not effected.
The de-icer 850 is a unitary structure that is joined to the propeller
blade 863 along bond line 862. The bond line 862 is preferably formed from
adhesive that positively bonds de-icer 850 and withstands centrifugal
forces during normal rotating use on a propeller. However, the adhesive
must also be easy to remove in the field. An example of a suitable solvent
based adhesive is 3M 1300L. The adhesive and de-icer must be removable
without damage to the propeller blade 863.
A bond layer 861 is formed from 0.016 inch thick neoprene. A compressible
member 853 is formed from butyl rubber and overlies the bond layer 861
over the apex 820. For a propeller blade, a width of about 3/8 inch has
been found to be satisfactory for the compressible member 853. The desired
width could change depending on the application and is empirically
determined. A release layer 859 having good dielectric properties, for
example 3M 204/3 teflon tape adherent on one side, is applied over the
surface of the target 860. A target 860, formed from 0.016 inch thick
copper sheet overlies the bond layer 861 abutting the compressible member
along one edge. A mirror image target (not in view) is similarly prepared
and overlies the bond layer 861 on the opposite side of the propeller
blade 863 (not in view).
A coil is formed by bonding a copper sheet to each side of dielectric
carrier 856. The dielectric layer 856 can be formed from synthetic rubber
such as Neoprene, about 0.015 inch thick. A photoresist coil pattern is
photographically applied to the surfaces of both copper sheets using a
negative. The bond side coil member 857 and breeze side coil member 855
are subsequently etched from the copper sheets in an acid bath. Materials
and techniques for applying photoresist and etching copper foil are well
known to those skilled in the art of etching electrical circuits. A mirror
image coil is similarly prepared for application to the opposite side (not
in view) of propeller blade 863. The two coils can be formed
simultaneously which permits the use of a continuous ribbon jumper 864
between coils. Power lead 867 is attached to the coil at electrical
connection 866. A ring terminal connector 869 is attached to power lead
867. Another power lead (not in view) is similarly applied to the mirror
image coil (not in view). Only two power leads are required if the planar
coil and mirror image coil overlying the opposite side of propeller blade
863 (not in view) are connected in series by jumper 864.
The coil assembly is encapsulated by a breeze side dielectric layer 854 and
a bond side dielectric layer 858. The mirror image coil is similarly
encapsulated. The breeze side dielectric layer 854 is formed from Fiberite
MXB 7669/120 glass. Applicant has found that a thin layer of glass
stiffens the planar coil and significantly improves its dynamic motion by
increasing the frequency response and maximum acceleration normal to the
surface. Bond side dielectric layer 858 is formed from 0.016 inch thick
neoprene. As shown in FIG. 8, the edges of the bond layer 861, bond side
dielectric layer 858, dielectric carrier 856 and breeze side bond layer
854 are staggered relative to each other around the perimeter of the
de-icer. Staggering the edges creates a tapered edge around the perimeter
of the de-icer 850.
A splicing strip 852 is applied over the compressible member partially
overlapping the breeze side dielectric ply 854 on each side of the member
(the breeze side dielectric ply on the opposite side is not shown). The
weave of splicing strip 852 is most preferably placed on a 45.degree.
angle relative to the chordwise direction of the propeller blade 863.
Finally, a surface layer 851 is applied covering the entire construction
as shown. The splicing strip 852 is formed from tightly woven nylon fabric
coated with neoprene. The surface layer 851 is formed 0.020 inch thick
neoprene. A leadtab 868 is formed by encapsulating power lead 867 between
bond layer 861 and surface layer 851. Additional neoprene fill strips (not
shown) can be laid along the power lead 867 to provide a smoother
step-off. Neoprene fill strip 870 can be used to step-off the ends of the
butyl strip compressible member 853. If desired, a layer 871 of catalogue
no. 8671 Scotch polyurethane protective tape produced by 3M can be used to
improve the erosion characteristics. The polyurethane film has a
self-sticking acrylic adhesive on one side which sufficiently bonds the
film to the surface layer 851. The polyurethane film can be replaced in
the field when required due to erosion without replacing the entire
de-icer 850. De-icer 850 is best constructed in a female tool starting
with surface layer 851. Construction techniques are well known to those
skilled in the art of rubber de-icer lay-up. The outer dielectric layer
854 must be cured to the planar coil before the coil is inserted into the
construction.
Although the invention has been described with reference to certain and
preferred embodiments, including the best embodiments, it would be
apparent to people skilled in the art of de-icing of aircraft that other
variations are possible which are obvious thereover. There variations are
intended to be included by the present specification and appended claims.
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